1. Technical Field
The present invention relates to a base metal pigment having excellent water resistance and dispersion stability in an aqueous medium, an aqueous base metal pigment dispersion liquid containing the base metal pigment, and an aqueous ink composition containing the base metal pigment.
2. Related Art
In the related art, as methods of forming a coating film having metallic luster on a printed matter, a foil press printing method using a printing ink or metal foil, in which gold powder or silver powder made of brass, aluminum microparticles, or the like is used in a pigment, a thermal transfer printing method using a metal foil, and the like have been used. However, these methods are problematic in that it is difficult to form a fine pattern or to apply these methods to a curved surface. Particularly, the foil press printing method is problematic in that on-demand properties are low, the application thereof to multi-product production is difficult, and the printing of a gradational metal tone is impossible.
Recently, a large number of application examples of an ink jet head in printing have been found. One of the application examples is metallic printing, and thus the development of an ink having metallic luster has been conducted. An ink jet method is advantageous in that it can be suitably applied to the formation of a fine pattern or the recording onto a curved surface. For example, JP-A-2008-174712 discloses an aluminum pigment dispersion liquid based on an organic solvent such as alkylene glycol, and a non-aqueous ink composition containing the same.
Meanwhile, in terms of global environment and human safety, there is a tendency that the development of an aqueous ink composition instead of a non-aqueous ink composition based on an organic solvent is desired. However, when an aluminum pigment, as a kind of base metal pigment, is dispersed in water, alumina is formed together with the generation of hydrogen gas by the reaction with water to cause a whitening phenomenon. For this reason, the aluminum pigment loses metallic luster.
In order to solve the above problems, for example, Japanese Patent No. 4358897 discloses a surface-coated aluminum pigment in which water resistance is provided by surface-treating an aluminum pigment with alkoxysilane. Japanese Patent No. 3869503 discloses a composition containing aluminum powder, inorganic phosphoric acid (salt), phosphate ester, and water. Japanese Patent No. 2759198 discloses an aqueous paint composition containing aluminum coated with a hetero-polyanion compound. JP-A-2006-199920 discloses an aluminum pigment, which is prepared by treating aluminum with a phosphate compound or a borate compound and then coating the treated aluminum with a layer containing hydrated tin oxide or the like.
However, the aluminum pigment disclosed in each of the above Japanese Patent No. 4358897, Japanese Patent No. 3869503, Japanese Patent No. 2759198, and JP-A-2006-199920 is problematic in that water resistance is insufficient, and in that surface state is changed by the oxidation proceeding over time in an aqueous medium, and thus dispersion stability deteriorates. In addition, when the surface of aluminum is coated, there is a problem in that the oxidation of aluminum proceeds during the surface coating, and thus agglomeration easily occurs together with the deterioration of luster.